Petroleum refineries often produce valuable distillates and coke by heating residual oil in coking drums. The process, known as delaying coking, involves severe operating conditions with high operating temperatures.
Coke drums are typically large, cylindrical vessels having a top head and a frustoconical bottom portion fitted with a bottom head. Coke drums are usually present in pairs so that they can be operated alternately. Thus, while one coke drum is being filled with residual oil and heated, the other drum is being cooled and purged of up to several hundred tons of coke formed during the previous recovery cycle.
Purging a drum of coke is sometimes referred to as “coke recovery”. In the prior art this often involved unbolting and removing the bottom head of the coke drum, and lowering it onto a cart for movement away from the path of the coke. In the more recent prior art pivots have been used to hydraulically move the coke drum head out of the way. Examples of such systems are described in U.S. Pat. No. 5,785,843 to Antalffy et al. (July 1998) and U.S. Pat. No. 6,264,829 to Antalffy et al. (July 2001). These and all other cited materials are incorporated herein by reference.
Still more recent art uses valves, referred to in the industry by the name deheader valves. Instead of unbolting the bottom coke drum head and either transporting or pivoting it out of the way to release the coke, the drum head is permanently replaced with a valve. U.S. Pat. No. 6,565,714 to Lah (May 2003) teaches that the valve can be coupled to the flanged portion of the coke drum. But that teaching does not address installation of the valve. There is no teaching or suggestion in that patent of how this could be done in a new or retrofit situation.
In retrofitting existing installations to use the new valves, problems arise with respect to installing the valves. One problem is that in installations designed for repeated bottom head removal, the bottom of the coke drum is positioned at some distance off the floor to allow for removal or swinging away of the bottom head. When the bottom head is replaced by a deheader valve, there remains a distance between the outlet of the valve and the floor that must be bridged in some manner. Another problem is that the outlet of existing coke drums is often larger than the inlet of the deheader valve (usually 72″ diameter vs. 60″ diameter). Still another problem is that the oil inlet in existing coke drums is usually located at a bottom blind flange. Elimination of that flange and installation of a deheader valve therefore necessitates providing another oil inlet to the coke drum.
The industry has solved all of these problems simultaneously by inserting a spool piece between the bottom outlet of the coke drum and the top inlet of the deheader valve. The spool piece serves to lower the height of the valve, thereby bridging most of the distance between the valve and the floor. The spool piece is also usually funnel shaped, adapting the larger drum outlet to the smaller valve inlet. Still further, the spool piece is provided with an oil inlet, thus replacing the oil inlet removed from the bottom blind flange.
Installation of a deheader valve using a spool piece is conceptually straightforward. The bottom drum head is removed, the spool piece is installed on the valve, and then the valve with spool piece is moved horizontally into position, and then raised so that it can be bolted onto the bottom of the coke drum. Since deheader valves typically weigh 35 tonnes, the floor of the installation usually cannot support the weight during installation and the valve is instead moved into position using a monorail or other overhead track.
In the prior art the distance that the valve and spool piece must be raised is always quite small, less than 2 cm. This is because the valve with spool piece is positioned under the drum with very little distance between the top of the spool piece and the drum flange. Raising the deheader valve this very small distance can be accomplished using spring hangers (spring cans). Indeed, in all installations of which we are aware, the deheader valve is raised using spring hangers. Although they have a limited range of motion, and move the valve quite slowly, spring hangers are also accurately controllable and well suited to the task.
Recently, the present inventors realized that it may be desirable to fit a deheader valve onto a coke drum without using a spool piece. In that instance, however, some other means must be adopted to provide an oil inlet for the drum, and some other means must be provided for raising the valve into place. Thus, there is still a need to resolve those problems.